It's going to take you over 500 hours to 100% complete Mewgenics, according to creator Edmund McMillen

By the time I came to post my Mewgenics review, I had over 100 hours logged in the game—and I knew I still wasn't completely done. Now, at about 115, I can at least see the light at the end of the tunnel when it comes to finishing off the main questline, but apparently I've still got a long, long way to go before I hit 100%.

According to creator Edmund McMillen, speaking in an AMA on the Steam Deck subreddit, "It will take an average player about 200+ hours to 'beat the game' and 500+ hours to 100%".